The present invention relates to a method according to which a variable air pressure value of a pneumatic vehicle tire is determined and transmitted. In so doing, an information signal that corresponds to the air pressure value is transmitted in a non-contact manner from a measured value emitter to a measured value receiver, with this signal being evaluated electronically or in a data circuitry or analyzer. The information signal is compared with desired values, at least for air pressure within the pneumatic vehicle tire, and a deviating measured value, including the value 0, is determined. An air pressure state corresponding to the measured value is then indicated. Such an air pressure state is preferably indicated to the driver of the vehicle for each vehicle wheel during operation.
To transmit a variable measured value for the tire pressure of pneumatic vehicle wheels, a method is known from German Pat. No. 30 29 563, dated June 20, 1985, corresponding to U.S. Pat No. 4, 567,459-Folger et al issued Jan. 28, 1986, according to which either the information signal is continuously independent of the tire pressure and an associated desired value is changed in conformity to the atmospheric temperature, or a constant desired value that is independent of the atmospheric temperature is only independent above a prescribed critical temperature, and below this critical temperature is dependent on the tire temperature.
The tire pressure is determined by the factors of atmospheric pressure, inner temperature of the tire, and specific air volume. With the heretofore known method, pressure and temperature are not taken into consideration as much as would be advisable in order to be able to give the best possible information to the driver.
A positive change of the atmospheric pressure results in a negative change in the tire pressure, with regional changes in the atmospheric pressure of up to 0.1 bar being possible, and without altitude differences changing the atmosphere pressure by only 0.1 bar per 1000 m. Temperature changes result in a directly proportional change in pressure, whereby, for example, at average passenger car tire air pressures, a 10.degree. C. temperature difference corresponds approximately to a 0.1 bar pressure difference. With large tires the pressure difference is even greater due to the higher air pressure that is provided. A positive change in volume effects a negative change in pressure that proportionately can be up to 1.5 times greater. The differences relative to the desired pressure that can result during a driving operation achieve up to 0.5 bar, even if a driver takes great care to regularly check the tire pressure. And if a driver doesn't regularly check the tire pressure as prescribed by the owner manual, the difference to the desired pressure can be even greater. And if the driver doesn't check the tire pressure at all for a long period of time, the difference to the desired pressure over a single season can be as much as 1 bar.
A method designed for determining the changed air pressure, and an evaluation for indicating the actual pressure state, should take into account the aforementioned factors. The systematic indication helps to assure a great active reliability, with reliability against tire failure, and improved constant driving conditions, being significant. The indication should furthermore offer improved maintenance convenience, by normally making it possible to increase the intervals between times when the air pressure has to be attended to. Furthermore, the tire pressure that can best be provided by indication helps to save energy by having a reduced resistance to rolling. There thus results a greater economy. In addition, the tire lasts longer due to more uniform wear.
It is therefore an object of the present invention, while taking into consideration the aforementioned facts, to provide a method for determining, evaluating, and indicating a constant or changed tire air pressure, whereby changing pressure and temperature influences caused by regional and seasonal conditions are reliably taken into account.
The information signals should be compared with appropriate desired values. The deviations determined by the evaluation should be indicated as the actual tire air pressure state. These pressure states, on the one hand, should include an air pressure range that is optimum for the driving operation, and on the other hand should include the excess pressure range disposed thereabove and the low pressure range disposed therebelow. In this way, in addition to values within the optimum range, values are also included from the ranges that no longer assure optimum driving safety and that improve driving comfort.